This invention relates generally to the field of methods and processing systems for treatment of large volumes of citrus peel or similar waste products to be converted into useable products and to extract desirable components for distinct applications. More particularly, the invention is such a method and system for the efficient removal of residual liquid and oil from the citrus peel, where a high percentage of available oil is recovered, a high percentage of the water is removed from the peel, the peel is fragmented into relatively small particles for subsequent processing, potential volatile organic contaminants (VOC's) are eliminated prior to the drying process, the resulting peel particles can be rendered food grade quality for human consumption, and where processing time, energy needs and costs are greatly minimized when compared to existing processes.
Nearly 50 billion pounds of citrus are processed each year, mainly to extract drinkable juices for the consumer market. The extraction of the juice creates a large amount of waste by-product in the form of orange peel, seeds, rag (the membranes between the citrus segments) and pulp. In the U.S., the waste organic material cannot be dumped into land fills, but instead must be converted into a useable product. The waste is primarily converted into citrus pulp pellets (CPP) for cattle feed, since the waste peel and other components provide filler and a protein source, although at only about 6% protein content it is not a high protein source food. Citrus oil contained within the peel is a marketable by-product, and current processing removes a relatively small amount (less than about 15% of the total available quantity) from the peel by extractors compressing the fruit sphere prior to removal of the juice and further processing. The oil is then further processed and refined and currently sells at about $0.35/pound in the form of cold press peel oil. The current technology for processing the waste peel operates at a loss--the costs are more to process the material than can be regained by selling the resulting products as a non-food grade material.
The current state of the art is a system which squeezes the peel to remove some of the citrus oil, slices the fruit in half, reams or presses the halves to remove the juice and pulp, and ejects the waste peel, rag, seed, etc. to a conveyor for transport to a peel processing plant. The peel is then delivered into fixed rotor blade hammer mills which rotate and thrash the peel in a very inefficient manner relative to particle size and rate control, with resulting particles ranging from one square inch pieces up to entire fruit halves. The thrashed peel is then placed into mixing augers where lime (calcium oxide) is added to dehydrate the peel; the lime contacts free water forming a basic anhydride reaction. Alternatively, the lime is sometimes applied prior to the hammer mill step. The result is an orange peel cake material containing about 80% residual water. The addition of the lime renders any subsequent products unsuitable for human consumption. The thrashed waste material is pressed, which removes approximately 10 to 15% of the free water along with some residual oil, which is called pressed liquor. The liquor is pumped to waste heat evaporators where water is evaporated to produce a low brix molasses of about 50 brix sugar content. This molasses is sprayed onto the cattle feed pellets produced from the peel particles to enhance the flavor and subsequent ingestion by beef and dairy cattle. The pressed peel particles are then passed through large, gas-fired, single-pass, low rpm (3-10), rotary dryers, typically about 18 feet in diameter by 80 feet in length, where predominantly gas fired air is heated to about 1500 degrees F. and raises the particle temperature to a range of about 290 to 700 degrees F. over the course of about 45 minutes. The high heat of the air in the dryer actually combusts or flashes off most of the volatile liquids and gases in the peel, emitting VOC's and associated hydrocarbons into the exhaust air to atmosphere. Burnt gases, liquids and solids coat and foul the interior ductwork and dryer contact surfaces, often leading to fires within the equipment and fan blade failures. Since the exhaust air contains a large amount of contaminants such as particulate matter, VOC's, oil, moisture, etc., the air flow must pass through scrubbers to remove a significant portion of the contaminants. The scrubbers typically utilize water sprays, which reduce the potentially recoverable heat energy of the exhaust air by about two thirds. This scrubbed air is then passed to heat recovery equipment, where the lowered heat value (about 180 degrees F.) is then used as the heat source in waste heat evaporators for the production of molasses. Currently, exhaust air must be scrubbed prior to passage through the heat recovery equipment to prevent plate surface fouling, which reduces performance and may cause failure. The dryer-discharged, dried peel matter has a moisture content of about 10 to 15% and is then pelletized into citrus peel pellets, ranging from about 3/8 to 1/4 inches in diameter and from about 1/4 to one and one quarter inches in length. The pellets are then sold as cattle feed at a price of about $40/ton, even though the processing costs to produce the pellets ranges from about $60-70/ton. The current systems utilize oil or natural gas combustion heating, are processes utilizing equipment which are not able to be cleaned on-line except by shutting down the process, are unable to recoup most of the exhaust heat energy, produce contaminated air which must be scrubbed prior to reuse or exhaust to the atmosphere, cannot remove any of the 85-90% residual citrus oil, and cannot produce a food grade product for human consumption due to the addition of lime during the process.
It is an object of this invention to provide a system and method which eliminates all or most of the drawbacks from the current waste peel processing and drying systems. It is an object of this invention to provide a waste peel collection, processing and drying system and methodology which incorporates on-line storage, continuous product temperature elevation and control, high-shear particle reduction and pumping to increase the exposed waste material surface area allowing more efficient removal of organic compounds prior to any drying steps which would release hazardous, volatile organic compounds into the exhaust gas and atmosphere, recovers a high percentage of reusable waste heat energy, and increases the recovery of usable by-products. These and other objects which are implied and inferred from the following disclosure are attained by providing a preferably continuous-flow processing system preferably incorporating live-bottom storage conveying equipment, flow metering with temperature elevation equipment, pulping equipment capable of creating small particle size from the waste peel, vibratory shaker table separating equipment to remove liquid from the solid waste particles, centrifuge equipment to remove water and solids from the oily liquid, press equipment to remove additional liquid, called liquor, from the waste particles, and dryer equipment to remove remaining moisture from the waste peel such that the waste may be pelletized or ground, with heat recovery means to extract the highest quantity of heat available from the dryer exhaust air to preheat air for the dryer, combustion air or air make-up, and to evaporate water from the pressed filtrate to produce citrus molasses.